Electrical measuring instrument



April 1,5, 1930. c. L. I IPMAN 1,755,009 l ELECTRICAL MEASURING INSTRUMENT Filed May l2, 1927 4 Sheets-Sheet l April 15,'1930. c. l., LIPMAN l ELECTRICAL MEASURING INSTRUMENT 4 Sheets-Sheet 2 Filed May 12, 1927 voL r/rf TER F/QS.

April A15, C, UPMAN 1,755,009

ELECTRICAL. MEASURING INSTRUMENT Filed May l2, 1927 4 Sheets-Sheet 3 DIFFERENTI/9L V04 TME'E? 1576.5 F76. 6- yoL TM5-rif? NNE' TER' April 15', 1930. c. L. I IPMAN l 1,755,009

y ELECTRICAL MEASURNG INSTRUMENT Filed May l2, 1927 4 Sheets-Sheet 4 M rfv? OVE/P Awa a/vof/P cfwPrr'f/vr E of? voLav-KEL4K 3 V VZ774 Zzmzz Zw @if/Zaza ZL 772.220

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Patented Apr. Vl5, 1930 UNITED STATES PATENT OFFICE CHMO'UL LEIIB- LIPMAN, OF LONDON, ENGLAND, ASSIGNOR OF .A PART INTEREST TO NALDER BBOTHEBS& THOMPSON LIMITED, OF LONDON, ENGLAND Application med May 12, 1927, Serial No. 190,948, and in Great Britain Hay-20, 1926.

gizing winding is provided on the outer laminated core of the electromagnet and one or more supplementary windings are provided on polar projections of the inner core' symmetrically arranged with respect to the polar surfaces of the outer core or on both inner and outer cores, 1n order to produce a' field or fields, which is or are displaced, both in space direction and time phase, relatively to that of the main winding, while other unwound or wound projections of the inner core reduce or increase the magnetic reluctance of the main field path.

The construction of the instruments is preferably such that all the windings are easily removable and exchangeable.

The polar projections of the inner core are symmetrically arranged and approach close to the internal surface of the drum; the projections are preferably, but not necessarily,

'30 in the form of a cross, windings being rovided in the latter case on one or botho they core may be of smaller cross section than that of the unwound projections in order to lessen the inductance of the circuit of the supple- J meter, voltmeter or Wattmeter, a differential or paralleling voltmeter, or as an over or under current or volt relay. v

In the case of a polyphase instrument two or three such electromagnetic elements are arranged to act on a common moving system.

mentary windings, and in special cases the A further object of the invention is to provide an instrument in which the effect-s of changes of temperature or changes of frequency of the current are compensated or substantially reduced.

A further object is to provideV means by which the range of the instrument or its sensitiveness can be controlled.

A further object is to provide means by which the phase relation between the field produced by the main energizing winding and the field produced by the supplementary winding or windings on the inner core may be adjusted. I y

The accompanying drawings illustrate diagrammatically examples of electrical instruments and relays according to the invention.

lig. 1 represents a single phase wattmeter an Fig. 2 shows on a larger scale the poles of the inner and outer core of the horseshoe shaped eleotromagnet.

Fig. 3 shows a voltmeter or over or under volt relay according to the invention.

. Fi 4 illustrates the form of drum or cylindrlcalv rotor adapted to be used for most ofthe instruments described.

Fig. 5 shows a diie'ren'tial voltmeter for use on a olyphase or single phase 3 wire systeni for )galancing or regulatin purposes.

Fig. '6 shows a voltmeter w ich is practically independent of errors due to variations of temperature.

Figs. 7 and 8 show preferred constructions of ammeters or overl or under current relays.

Fig. 9 illustrates a preferred form of shaped drum or rotor used in conjunction with an amineter.

Fig. l0 shows a modified form of ammeter which is practically free from errors due to changes in temperature.

Fig. l1 represents a modification of the invention as applied to over or under current or volt relays.

Referring to Figs. l and 2, V1, V2 are the terminals of the potential winding V of a single phase wattmeter; the windings are wound on a bobbin A placed on the yoke B of the laminated magnetic core B, B1, B2 of an electromagnet. The yoke B is formed scparately from the limbs B1, B2, so that the yoke with the bobbin can be inserted in poition between these limbs. A hollow cylindrical drum D, preferably of thin aluminium or copper, is mounted on a pivoted spindle shown in section at d and is adapted to be set into rotational movement between the poles E1, E2 of the electromagnet. The magnetic circuit is completed by an inner core F, which in the example illustrated is of cruciform shape, placed symmetrically with respect t0 the oles E1, E2 of the electromagnet and coaxlal with the drum D.,

In the construction illustrated` the axis of the two polar projections F2. F4 is in line with the central portions of the external poles E1, E2, thus providing a magnetic path of reduced reluctance for the main flux.

Bobbins G1, G2, shown in section in Fi 2. are placed on the poles F1, F2 of the core F and contain a few turns of wire C1. C2 con` nected to the current terminals M. L of the load circuit. The bobbins G1, G2 may be omitted if the coils C1, C2 are suitably wrapped with insulating material.

The windings C1, C2 may be connected in series or in parallel or in opposition, or in some cases one of these windings may he omitted. 4

The core F is built up of laminated plates of magnetic material; the polar projections may take any required form, and the crosssection of the parts F1, F2 on which the current windings are mounted is, preferably, considerably less than that of the parts F2, F which are in line with the poles E1. E2.

The main magnetizing winding V produces a flux shown b v the chain lotted lines. and the windings C1, C2 produce a flux shown by the broken lines these two fluxes are at right angles where they traverse the drum D.

Since the potential winding V consists of a large number of turns and the magnetic. reluctance of its circuit is very small. there is a considerable inductance and time-phase lag in this circuit. whereas in the circuit ot' the current windings C1. C2. owing to the small number of turns and the reduced seetion of the parts of the core on which they are wound and the comparativelv large air gaps between the poles F1. F2 and the poles E1, E2. the inductance is small and consequently the flux due to the current coils is practically in phase with the current producing it.

An auxiliary winding K short circuited on itself or through a resistance ll may be placed in known manner at any part of the in agnetie path B, B1, B2 or according to the invention on the internal poles F2. F1 in order to make the angle between the two fluxes exactly equal to 90. thus ensuring a perfectly uniform resultant rotating tield which tends to rotate the drum D in a given direction against an opposing torque such as that of a spring.

The torque exerted on the moving members can be adjusted in a simple manner by means of a magnetic shunt, consisting of a strip e (Fig. 7) of magnetic material of suitable dimensions placed near to the poles E1, E2 of the eleetromagnet in order to divert a portion of the lines of magnetic force. This is useful in equalizing the torque due to the ele ments of a polyphase instrument.

In Fig. 3, which illustrates the instrument constructed in its simplest form as a voltmeter. the coil C1 is of fine wire and is lconnected in series with a high non-inductive resistance R and in shunt with the highly inductive winding V across the terminals V1. V2 of the instrument. The same construction can be used as an over or under volt relay with the addition of suitable contactsand the like.

Fig. 5 illustrates a diilerei'itial voltnieter for indicating, .for example, whether the voltage of one portion of a polyphase system is equal to or is above or below that of another portion of the same s vstem. Coils H1, H2, H" are placed on suitable projections or pole shoes of the poles E1,- E2 close to the'drum and are energized through a non-inductive resistance R1 from the secondary winding S of a transforming device, the primary winding of which is V. The coil V is connected to the terminals V1,- V2 which are connected across one portion or phase of a polyphase system either directly or through a potential trailsformer. The electrical connections are such that the resultant rotating field due to the windings V and H1, H2, H2, HL exerts n. torque in a given direction upon the moving system, for example in the anticlockwise direction.

vThe coils C1, C2 mounted on the poles F1, F2 of the inner core. are connected in series with a suitable impedance R2 across terminals M1, M2 which are connected across another portion of a polyphase system. the voltage of which it is desired to compare with that between V1 and V2. u

The electrical connections are such that the resultant rotating field due to the coils V and C1. C2 exerts a torque on the drum in the opposite direction to that of the field due to the coils V and H1. H2. H2, H.

It is obvious that when all the windings are energized sinniltazuously a pointer connect ed to the drum D will give readings proportional to the difference in volts between the two sources of voltage.

The moving s vstem is preferablyv controlled by a hair spring 7 which is arranged to indicate a zero reading at the centre of the scale.

The electrical circuits can be so adjusted that. when euual volts are applied to the terminals Y1. V2. and M1. )l2 respectively. the opposing magnetic fields will also tend to set the pointer at the centre of the scale.

llO

`flhevvindings V and S are shown in'Fig. Vside by side,.hut in practice they are prefi erahly Wound concentrically.

It will he understood that it is Within the scope of theinvention to employ additional windings and to place them on the ends F3, F of' the core F, andto arrange the electrical constants of their circuit so as to produce aA linx hearingv any/desired time-phase relation to `that produced hy the remaining` coils.

In Fig. 6 which illustrates the construction of a Toltmeter that is practically independent of errors dueto variations of temperature, the coils C1, C2 inseries with a resistance R2 are connected across the secondary winding S to which the coils H1, H2, H3, H4 and resistance R1 are 'also connected. p

lThe action of the windings is differential and similar `to that described with reference toFig, 5except that the total ampere turns oli the compensating coils H1, H2, H3, H* are only a small percentage ofthose of the principal coils C1, Cg 'andthat the instrument is provided vvth a Zero at one end of the scale and two terminals only.

ln order torender the instrument free from temperature errors, due either to external or internal effects, the windings of the coils Hl-H and Cl--C2 may he, as usual, of copper and the resistance R1 Wholly or partially of copper or of other material in which' theresistance is relatively largely affected by temperature, the resistance R2 on the other hand'consists of a material having a very small or. negligible` temperature resistance coefficient, such ,as thel high resistance alloy of co per and nickel known as Eureka.

` he resultant action depends upon the dif- 4ference between the efect'due to the coils C1, C2 and that due to thev coils lll-H4 of Whichthat'of the latter is smaller than and opposed to the former.

, 'If the temperature rises, the resistance of both coils will be increased and the currents in them reduced and, omitting;r the etlect of the resistances R1, R2 in the saine ratio. It the action of both coils is reduced in thc` same ratio, the resultant effect will be similarly reduced and tomaintain it at a constant value it is necessary to reduce the opposing force due to the coils HL-H2 in a great-er ratio than the force due to the coils C1, C2. This is effected by the use of a. material for the resistance R1 which is more aiiected by temperature than the material of the resistance R2. The values of the resistances Rl. R2 are determined empirically hysuitable trials.

In Fig. 7, which represents a simple form of construction ot an amuieter. the coil C2 on the pole F2 of the inner core F is connected to the secondary winding S of the main electrolnau'net either directly or in series with a resistance R2. The primary winding' l) is connected in the'extcrnal load circuit either directly or through a current transformer.

Fig. 8 illustrates an alternative construction of an ammeter which is similar to that of except that supplementary coils H2, H4 are added on the lower pole shoes of the oles E1, E2. l2, H* is such that they assist one another and produce a common fiux the intensity of which is'greatest in the region of the Wound poles. rlhis concentration of flux at a particular part of the magnetic system is advantageous Awhen used in conjunction with a suitably shaped or slotted rotor, the combination tendinfnr to give a uniform scale of deflections on an instrument, the operating forces of which are proportional to the square or other power oi the quantity to he measured.

An ammeter constructed in accordance with F igs. 7 or 8 will indicate accurately in'- dependently of the frequency of the alterna tions. Y

Since the torque on the drum D is proportional to the product of' the main magnetic linx, frequency and current in the secondary circuit in the coil C2, or coils C2, H2, H4, the force exerted upon the drum with any given current through the primary P remains constant for any frequency, since a cha-nge of frequency will vary the main flux in the inverse ratio and the secondary current is prac tically the same at all frequencies for a given primary current, and hence the product of the three quantities remains constant.

The primary and secondary windings form a transformer in which consequently the secondary current hears a constant ratio to the primary current. For a given value of the primary current, the secondary current will have a constant value, but as the resistance of the primary circuit is practically negligible compared with its inductanee, the main field is reduced in the ratio of the change of frequency.

The constructions shown in Figs. 7 und 8 illustrated also the invention as applied to an over or under current relay.

Fig. 10 illustrates an ammeter which is compensated against errors due to changes in temperature and is similar in its mode of action to that shown in Fig. 6;

The principal system consists of a coil C2 on the pole F2 which is energized from the secondary winding S either directly or in series With a resistance R2. The compensating system in the example illustrated consists of a coil H2 on the lower left hand pole shoe in series with a suitable series resistance R1. The compensating system is shown in Fig. l0 as connected in parallel with the Windings on the internal core, but, alternatively, it could also he energized directly from the terminals M, L in shunt with the primary coil P of the electromagnet. 4

In some cases an additional colnpensatin,"y resistance R3, the material of which has the required temperature (resistance) coeiicient,

The polarity ot the coils C2,

iss

windingl.

As in Fig. 6 the two system of supplementary windings act in opposition to one another and the torque due to the principal coil C considerably exceeds that due to coil H, whereas the materials for these windingsl are so selected and proportioned with respect to their temperature resistance coflicients that changes of temperature affect the two systems equally, thus neutralizing any errors due to this cause, independently of the characteristics of the current to be measured.

In Fig. 11 which is generally similar to Fig. 8 an/additional switch or plug connector T 1s provided whereby any desired number of supplementary coils may be energized from the winding S. By means of this a large number of ranges can conveniently be provided in one instrument. Suitable resistances rl-r may be included for calibration purposes in each winding.

Having thus described the nature of the said invention and the best means I know of carrying the same into practical effect, I claim 1. An electric alternating current instrument comprising an electromagnet, a laminated core for said magnet, a main energizing winding on the said core, symmetrically disposed polar surfaces on said magnet, a drum of electric conducting material adapted to be rotated through an arc between said polar surfaces, a fixed inner core of magnetic material within said druln, polar projections on said inner core and a winding on one of said polar projections of said inner core extending close to the inner periphery of said drum arran ed and connected to produce a magnetic fieli in said polar surfaces substantially at right angles in time phase and space direction to that produced therein bythe said main magnetizing winding.

2. An electric alternating current instrument according to claim 1, in which the projections of the inner core are of cruciform shape and two of said projections are disposed in the axis of said polar surfaces.

3. An electric alternating current instrument according to claim 1, in which a supplementary winding is provided on the projection of the inner core on the same axial line as the first-named projection, the supplementary windings beingr connected in series and energized inductively from said energizing winding.

4. An electric alternating current instrument according to claim 1` in which a closed Winding is provided n the core of the said magnet and an adjut-sable resistance is inserted in said Winding in order to adjust the phase relation between the main and supplementary magnetic fluxes.

5. An electric alternating current instrument according to claim 1, in which a pole shoe is provided eccentric to the axis of the olar surfaces and a supplementary windmg thereon is inductivel energized from said main energizing win ing.

(i. An electric alternating current instrument according to claim 1, in which a pole shoe is provided eccentric to the axis of the polar surfaces and a supplementary winding on said pole shoe is inductively energized rom the main energizing winding, and resistances of suitable materials are inserted in said su plcmentary windings in parallel with t e main energizing winding in order to compensate efl'ects due to changes of frequency and temperature.

7. An electric alternating current instrument according to claim 1, in which a pair of pole shoes is provided 011 each polar surface eccentric to the axis of the said surfaces, and supplementary windings on said shoes are connected in series with the said supplementary windings on the inner core and energized inductively from the main energizing winding.

8. An electric alternating current instrument comprising a horseshoe sha ed electromagnet, a laminated core for sai magnet, a source of alternating current, a main energizing winding on the said core connected to said source, a secondary winding energized from said main winding, two symmetrically disposed polar surfaces on said core, a drum of electric conducting material adapted to be rotated through an arc between said polar surfaces, a fixed inner core of magnetic material having four rectangularly disposed projections, the axes of two of said projections lying in the direction of the axis of the said polar surfaces, supplementary windings on the projections at right angles to the said axis, a pair of pole shoes on each polar surface, eccentrically disposed to said axis, supplementary windings on said pole shoes, all said supplementary windings being adapted to be connected in series with said secondary winding.

9. An electric alternating current instrumentcemprising a horesshoe shapel electromagnet, a laminated core for said magnet, a source of alternating current, a main energizing winding on the said core connected to said source, a secondary winding energized from said main winding, two symmetrically disposed polar surfaces on said core, a drum of electric conducting material adapted to be rotated through an arc between said polar surfaces, a iixed inner core of magnetic material having four Ireetangularly disposed projections, the axes of two of said projections lying in the direction of the axis of the said polar surfaces, supplementary windings on the projections at right angles to the said axis, a pair of pole shoes on each polar surface, eccentrically disposed to said axis, supplementary windings on said pole shoes, and

Vterial having four rectangularly disposed `of electric conducting material adapted to means including a movable contact arm for connecting any requiredv sets of supplementary windings in series to said secondary winding.

10. An electric alternating current instrument comprising a horseshoe shaped electromagnet, a laminated core for said magnet, a source of alternating current, a main energizing winding on the said core connected to said source, a secondary winding energized from said main winding, two symmetrically disposed polar surfaces on said core, a drum of electric conducting material adapted to be rotated through an arc between said polar surfaces, a fixed inner core of magnetic maprojections, the axes of two of said projections lying in the direction of the axis of the said polar surfaces, supplementary windings on the projections at right angles to the said axis, a pair of pole shoes on each polar sur-5 face, eccentricall disposed to said axis, su plementary win ings on said ole shoes, a said supplementary windings eing adapted to be connected in series with said secondary winding and means by which effects due tb changes of frequency and temperature can be compensated.

11. An electric alternating current instru- `f ment comprising a horseshoe shaped electromagnet, a laminated core for said magnet, a source of alternating current, a main energizing winding on the said core connected to said source, a secondary winding energized from said main winding, two symmetrically disposed polar surfaces on said core, a drumf be rotated through an arc between said polar surfaces, a fixed inner core of magnetic material having four rectangularly disposed projections, the axes of two of said projections lying in the direction of the axis of the said polar surfaces, supplementary windin on the projections at right angles to the said axis, a pair of pole shoes on each polar surface, eccentrica ly disposed to said axis, supplementary Win ings on said pole shoes, all said supplementary windings being ada ted to be connected in series to said secon ary winding, and means .by which the angular relation between Vthe magnetic iiuxes due respectively to the main and supplementary windings can be adjusted.

In testimonywhereof I have signed my name to this s eciication.`

c oUL LEIB LIPMAN. l 

